Kobo's devices let you bypass the account signup via a single option in a config file. Whether you do so or not it's easy to install koreader and start writing plugins for it. You can also hack on the linux OS they use
Been super happy with my Kobo Clara.
Got a USB expander dongle on AliExpress for something like six bucks that breaks out a few USB 2 ports and the Kobo is happy as a clam. So am I now, because the Kobo is great.
It’s not too disgusting, and over-the-air is nice to have.